1. Technical Field
This invention relates generally to sailing yachts, and more particularly to externally ballasted high performance sailing yachts.
2. Description of Related Art
Typically, external ballast is located at the lowest point on rigidly fixed keels. The keel serves two functions—it supports the external ballast and it provides a high aspect lifting surface to keep the vessel from sliding sideways as it sails upwind. As the vessel heels, the ballast works to counteract the force of the wind. There is no restoring force until some angle of heel is generated. As vessels heel, the effective area of the lifting surface reduces, comprising the windward performance. Attempts to reduce the angle of heel, center on moving ballast. Two typical methods of moving ballast to the windward side of the vessel include the swing keel and internal water ballast. The swing keel mounts ballast on the bottom of the keel, using the keel as a moment arm to increase the effectiveness of the weight in generating a righting moment. Water ballast using pumps to fill bladders inside the hull as needed to adjust trim. Since the water is inside the hull the moment arm to the center of buoyancy is short, requiring significantly more weight to an equivalent righting moment.
U.S. Pat. Nos. 5,163,377 and 5,622,130 describe various aspects of a keel-less sailing yacht that has fore and aft cambered foils for leeway control and a dynamic gravitational ballast for heeling resistance. A ballast-supporting structure, in the form of an elongated strut extending downwardly from the hull, supports the ballast generally beneath the hull. Twin fore and aft rotatable foils are also supported by the hull with extension below the hull for optimum performance under a wide range of operating conditions, preferably being controlled by a hydraulic or electric system.
A keel-less sailing yacht with appendages in the form of a movable ballast-supporting strut and twin fore and aft foils is sometimes referred to as a canting ballast twin foil (CBTF) sailing yacht. Such CBTF sailing yachts enjoy recognized sailing success accompanied by significant interest in CBTF technology. However, various structural and operational concerns need attention.
For example, the downwardly depending foils and ballast-supporting strut hinder operations in shallower water. In addition, replacement of foils damaged by vessel grounding is impaired. Furthermore, operating performance of larger sailing yachts, including those designed for ocean racing or cruising, can suffer somewhat under various sailing conditions (e.g., sailing off wind) due to the friction drag introduced by the downwardly depending appendages. Thus, a need exists for CBTF improvements in these respects.
U.S. Pat. No. 6,886,481 describes a pivotable deployable bulb mounted foil apparatus for a sailboat whose foils can be deployed from a nested position and pivoted when needed for lateral resistance. This invention is especially adapted to a canting keel where the sailboat loses its lateral resistance from the keel when the keel is canted.